This invention relates to papermaking and particularly to the treatment of cellulosic material preparatory to use of the treated material to manufacture paper web material.
As is well known in the art, paper is commonly formed from wood. Generally, the industry divides wood used in papermaking into two categories; namely hardwoods and softwoods. Softwood fibers (tracheids) come from needle-bearing conifer trees such as pine, spruce, alpine fir, and Douglas fir. Hardwood fibers are derived from deciduous trees of various varieties.
Among the distinguishing differences between hardwood (HW) fibers and softwood (SW) fibers are (a) the length of the individual cellulosic fibers of the wood, (b) the coarseness of the fibers, and (c) the stiffness or collapsibility of the fibers.
The morphology of softwood fibers, tends to limit the potential uses of the papers producible from such fibers. “Paper” as used herein includes webs or sheets without limitation as to the size or basis weight of the web or sheet. For example, either HW or SW paper may be employed as “bleached board” (useful in containers for consumer products, for example) or as “container board” or “liner board” (useful in corrugated boxes, for example). Printability of a paper is a major consideration with respect to the end use of the paper. SW fibers are notoriously problematic as respects the printability of the paper produced from these fibers in that SW fiber papers tend to be inordinately porous, stiff, and must be treated specially to obtain a paper surface which is suitably printable.
It is well known in the art that HW and SW must be subjected to specific treatments for converting the wood into a fibrous slurry employed in the formation of a paper web. Softwoods are more plentiful and are more readily replaceable, as by tree farming. Softwoods in general are less costly. Thus, it is desirable that SW fibers be substituted for HW fibers wherever possible in papermaking. Southern pine, or mixtures of hardwoods and softwoods, are commonly examined as possible substitutes for end products which have heretofore been manufactured using hardwoods.
Heretofore, in attempts to utilize SW fibers in printable paper, it has been proposed to treat the pulped fibers with hydrolytic enzymes. Refining of the enzyme-treated fibers to alter their size, shape, degree of fibrillation, etc., have been employed. Enzyme treatments suffer from sensitivities of the enzyme to process conditions, and a tendency to become inactivated and/or to be carried forward into the papermaking equipment. The lack of cost-effectiveness has also been a long-standing issue.
Chemical treatments, such as hydrogen peroxide treatment, are commonly carried out under alkaline conditions for bleaching or brightening of wood pulps. This condition that is maximized for bleaching, usually does not correlate with the best conditions for maximum oxidation.
Smoothness and Formation are measures of, among other things, the printability of the paper. “Formation”, as used as a paper characteristic usually, and herein, is a synonym for relative uniformity over a scale of some distance, e.g., 5 to 20 mm. Formation may be judged by viewing it with light from the back and other means. Both smoothness and formation are affected, among other things, fiber length, morphology and collapsibility.